Most ocular diseases are treated with topical application of solutions administered as eye drops or ointment. One of the major problems encountered with the topical delivery of ophthalmic drugs is the rapid and extensive pre-corneal loss caused by drainage and high tear fluid turn over. After instillation of an eye-drop, typically less than 2-3% of the applied drug penetrates the cornea and reaches the intra-ocular tissue, while a major fraction of the instilled dose is often absorbed systematically via the conjunctiva and nasolacrimal duct. Another limitation is relatively impermeable corneal barrier that limits ocular absorption.
Ocular drug delivery is an approach to controlling and ultimately optimizing delivery of the drug to its target tissue in the eye. Most of the current formulation efforts aim to maximize ocular drug absorption through prolongation of the drug residence time in the cornea and conjunctival sac as well as to slow drug release from the delivery system and minimizing pre-corneal drug loss. However, most of the current formulation efforts have a blurring effect on vision.
Liposomes have been studied for ocular delivery. However, a limitation of using liposomes for ocular drug delivery is the surface charge of liposomes. Positively charged liposomes seemed to be preferentially captured at the negatively charged corneal surface compared to negatively charged liposomes. Another limitation of liposomes is the instability of the lipid aggregates on the mucine surface.
There have been studies on the use of co-polymeric formulations for delivery of ophthalmic drugs. The pharmaceutical efficacy of these co-polymeric formulations depends on the specific nature and properties of the co-polymeric materials and the compound used. Moreover, the long residence time and sustained release of drug on cornea surface have not been achieved by co-polymeric formulations.